The present application relates to an illumination apparatus including a light transmission film on a surface of which prism structures are continuously arranged, and a liquid crystal display apparatus.
A liquid crystal display (LCD) apparatus can realize lower power consumption and reduction in size and thickness as compared to a cathode ray tube (CRT), and thus is currently widely used for a large-size LCD television, compact apparatuses such as a mobile phone, a digital camera, and a personal digital assistant (PDA), and like other products of various sizes.
The liquid crystal display apparatuses are categorized into, for example, a transmission type and a reflection type. In particular, the transmission-type liquid crystal display apparatus includes a liquid crystal display panel, a light-incident-side polarization plate, a light-exit-side polarization plate, and a backlight unit as an illumination light source. The liquid crystal display panel is formed by sandwiching a liquid crystal layer by a pair of transparent substrates. The light-incident-side polarization plate and the light-exit-side polarization plate are disposed on a light incident side and a light exit side of the liquid crystal display panel, respectively. The backlight units are categorized into a direct type backlight in which the light source is disposed immediately below the liquid crystal display panel and an edge-light type backlight using a light guide panel.
On the other hand, there has been known a structure in which a light transmission film referred to as a prism sheet is disposed between the backlight unit and the liquid crystal display panel in order to distribute outgoing light from the liquid crystal display panel so that the light has a large intensity toward the front. The prism sheet includes a prism portion formed by arranging a plurality of structures, each of which has an approximately triangular cross section and has a ridge line extending in a first direction (ridge line direction), in a second direction (arrangement direction) perpendicular to the first direction. The prism sheet exhibits an operation of improving a front luminance by causing light from the backlight unit to travel toward the front.
Further, Japanese Patent Application Laid-open No. 2002-90717 discloses an edge-light type illumination apparatus including a light guide panel and having a structure in which the prism ridge line direction is parallel or approximately parallel to a transmission axis of a polarization plate disposed on the light incident side of the liquid crystal display panel, and a liquid crystal display apparatus including the edge-light type illumination apparatus. On a light-exit-side surface of the light guide panel, a prism array in which prisms each having a triangular cross section are continuously arranged is formed.